Predators and parasitoids (a.k.a., natural enemies) are thought to be the primary agents keeping spruce budworm populations low during the years between outbreaks. These agents are also thought to be primarily responsible for driving populations back to low density at the end of an outbreak. Considerable work in the past 50 years has been dedicated to understanding the relationship between these natural enemies and the spruce budworm; however, our understanding of these interactions remains poor for rising spruce budworm populations.
A key part of our research project is to determine whether insecticide treatments are able to suppress low density spruce budworm populations, and whether these treatments have unwanted impacts on natural enemies. We have areas near Hornes Gultch, NB that were recently treated with the insecticide Mimic (completed June 24, 2014). While we have strong evidence that this insecticide has no impact on mammals, fish, birds, etc., we do know that it could impact other moth larvae that happen to also be feeding in the area, which in turn could affect any natural enemies they might be harbouring. Any significant impact natural enemies in non-target insect larvae could have a negative influence on the effectiveness of the Early Intervention Strategy as it could disrupt communities of these important natural control agents.
To investigate this issue, we have during the past few weeks been sampling branches for spruce budworm and other insects using pole pruners (Picture 1). Processing involves careful examination of each new shoot for any larvae they might be concealing (Picture 2). Spruce budworm, as well as any other insect larvae found, are placed in a container and frozen and will later be analyzed using new DNA technologies to determine what parasitoids or diseases are being carried the larvae. By sampling repeatedly throughout the season, we should be able to better understand the impact of different natural enemies on spruce budworm survival and associated population rise. Sampling and processing will continue every two weeks until pupation. Because we are collecting branches from both Mimic treated and untreated areas, we will be able to determine the impact of Mimic treatment on these potentially important interactions in the local insect community.
In the coming weeks, once the adult spruce budworm start emerging to lay eggs, we will begin our monitoring of migration events throughout the Atlantic region. More discussion of adult monitoring will come in the next post.